Replacing Transom

[Dagojoe]

Finally starting to replace the transom on my 1994 Lund. Fortunately I have 3 people helping me. All three are a lot more mechanical than me and one of them replaced his transom before. First day we pulled the motor and dug out the old transom in about 5 hours. Fortunately I did not have to remove the splash well but did have to cut a hole to get to one of the tow hooks. I guess I should say we vacuumed most of the transom out because it was pretty bad. Lucky my 115 hp motor did not fall off. We made a template out of thin Luan. My nephew has a 1" Cement Form Board left over from when he did his transom. I am going to buy 1/2" Marine Plywood because my haul was 1 1/2". I am planning on screwing the boards together with 1 1/4 coated deck nails. My question is, Should I also glue the two boards together and if so what would you recommend? Also, I am assuming I should coat the edges of the two boards. Was thinking about using Marine grade below the water line epoxy. Good? Thanks in advance for your advice.

 

[dozerII]

Glue the two plys together with Gorrilla polyurethane glue, ( make sure to lightly dampen one surface so it cures) To seal the wood, If you use epoxy you will have to use a thin coating one that will penetrate the wood or you can do like I do and give it three good coats of Spar Varnish, soaking the edges very well.

 

[jigngrub]

The marine grade epoxy resin will be your best build, use it to glue the boards together and coat both faces and all the edges of the plywood core with 4 coats.

 

[Dagojoe]

Thanks Glen and Jinngrug for responding. Looks like there are multiple options. question for both of you.

Glen, if I go this route, what would I use to thin it and what do you think the mix ratio would be for the first coating? I am also assuming the Spar Varnish would need to be specific for under waterline usage?

Jinngrub: I am using cement form board (that I am getting for free) as part of the total board. I believe this board has like a waxy surface. Do you know if the epoxy resin will stick to that?

 

[jigngrub]

Jinngrub: I am using cement form board (that I am getting for free) as part of the total board. I believe this board has like a waxy surface. Do you know if the epoxy resin will stick to that?

Cement form board sounds like either BB plyform or MDO plywood.

Nothing will stick to BB plyform, it is coated with a concrete release agent (oil) at the factory where it's made. No sealers, coatings, resins, or adhesives will work with BB plyform. Just screw it together and use it "as is".

MDO plywood has a very smooth fabric/paper like face with a phenolic coating... phenolic coating = epoxy. Marine grade epoxy resin will work very well with MDO plywood.

 

[gm280]

Cement board is going to be very heavy indeed. How to attach the actual plywood on is going to be the real problem. I do hope you understand that the cement board will not be a great surface to "glue" the plywood too. And I don't know how you're going to seriously seal all of that to protect it from water intrusion. Seems like if any water got in between the cement board and the plywood, it would stay there forever. But that is just my opinion.

 

[Dagojoe]

Thanks for the reply Jinngrub. gm280 - Thanks for the reply. Its not cement board but cement "form" board. I will double check with my nephew but I believe Jinngrub was correct in his reply. I will have to see what the coating is made of. If its the BB plywood I may rethink using it because I would never be able to glue together or coat the edges of the two boards. I will do more research. Thanks guys